SYNOPSIS

DESCRIPTION

BUGS

AUTHORS

**libpathplan**
− finds and smooths shortest paths

#include <graphviz/pathplan.h> typedef struct Pxy_t { double x, y; } Pxy_t; typedef struct Pxy_t Ppoint_t; typedef struct Pxy_t Pvector_t; typedef struct Ppoly_t { Ppoint_t *ps; int pn; } Ppoly_t; typedef Ppoly_t Ppolyline_t; typedef struct Pedge_t { Ppoint_t a, b; } Pedge_t; typedef struct vconfig_s vconfig_t; #define POLYID_NONE #define POLYID_UNKNOWN int Pshortestpath(Ppoly_t *boundary, Ppoint_t endpoints[2], Ppolyline_t *output_route); vconfig_t *Pobsopen(Ppoly_t **obstacles, int n_obstacles); int Pobspath(vconfig_t *config, Ppoint_t p0, int poly0, Ppoint_t p1, int poly1, Ppolyline_t *output_route); void Pobsclose(vconfig_t *config); int Proutespline (Pedge_t *barriers, int n_barriers, Ppolyline_t input_route, Pvector_t endpoint_slopes[2], Ppolyline_t *output_route); int Ppolybarriers(Ppoly_t **polys, int n_polys, Pedge_t **barriers, int *n_barriers);

**libpathplan**
provides functions for creating spline paths in the plane
that are constrained by a polygonal boundary or obstacles to
avoid. All polygons must be simple, but need not be
convex.

**int
Pshortestpath(Ppoly_t *boundary, Ppoint_t endpoints[2],
Ppolyline_t *output_route);**

The function *Pshortestpath* finds a shortest path
between two points in a simple polygon. The polygon is
specified by a list of its vertices, in either clockwise or
counterclockwise order. You pass endpoints interior to the
polygon boundary. A shortest path connecting the points that
remains in the polygon is returned in *output_route*.
If either endpoint does not lie in the polygon, -1 is
returned; otherwise, 0 is returned on success. The array of
points in *output_route* is static to the library. It
should not be freed, and should be used before another call
to *Pshortestpath*.

**vconfig_t
*Pobsopen(Ppoly_t **obstacles, int n_obstacles);
Pobspath(vconfig_t *config, Ppoint_t p0, int poly0, Ppoint_t
p1, int poly1, Ppolyline_t *output_route);
void Pobsclose(vconfig_t *config);**

These functions find a shortest path between two points in the plane that contains polygonal obstacles (holes).

`Pobspath`
finds a shortest path between the endpoints that remains
outside the obstacles. If the endpoints are known to lie
inside obstacles, `poly0` or `poly1` should be
set to the index in the `obstacles` array. If an
endpoint is definitely not inside an obstacle, then
`POLYID_NONE` should be passed. If the caller has not
checked, then `POLYID_UNKNOWN` should be passed, and
the path library will perform the test. The resulting
shortest path is returned in *output_route*. Note that
this function does not provide for a boundary polygon. The
array of points stored in *output_route* are allocated
by the library, but should be freed by the user.

**int
Proutespline (Pedge_t *barriers, int n_barriers, Ppolyline_t
input_route, Pvector_t endpoint_slopes[2], Ppolyline_t
*output_route);**

This function fits a cubic B-spline curve to a polyline
path. The curve is constructed to avoid a set of
*n_barriers* barrier line segments specified in the
array *barriers*. If you start with polygonal
obstacles, you can supply each polygon’s edges as part
of the barrier list. The polyline `input_route`
provides a template for the final path; it is usually the
`output_route` of one of the shortest path finders,
but it can be any simple path that doesn’t cross any
barrier segment. The input also allows the specification of
desired slopes at the endpoints via *endpoint_slopes*.
These are specified as vectors. For example, to have an
angle of *T* at an endpoing, one could use
*(cos(T),sin(T))*. A vector (0,0) means unconstrained
slope. The output is returned in *output_route* and
consists of the control points of the B-spline. The function
return 0 on success; a return value of -1 indicates failure.
The array of points in *output_route* is static to the
library. It should not be freed, and should be used before
another call to *Proutespline*.

**int
Ppolybarriers(Ppoly_t **polys, int n_polys, Pedge_t
**barriers, int *n_barriers);**

This is a utility function that converts an input list of
polygons into an output list of barrier segments. The array
of points in *barriers* is static to the library. It
should not be freed, and should be used before another call
to *Ppolybarriers*. The function returns 1 on
success.

The function
*Proutespline* does not guarantee that it will preserve
the topology of the input path as regards the boundaries.
For example, if some of the segments correspond to a small
polygon, it may be possible that the final path has flipped
over the obstacle.

David Dobkin (dpd@cs.princeton.edu), Eleftherios Koutsofios (ek@research.att.com), Emden Gansner (erg@research.att.com).